And the question: is what i should put into %UNIT%?
It's new for me and i don't know where ouf/ouf_layout stores "unit" and how to get it.
I tried some variants, but no results. And search didn't give me results too, mb cos of my bad english. ;(

No. If you add a UnitAffectingCombat check there, you will never see a Combat icon, because the frame is created before anyone is in combat, so the check will prevent the Combat icon from being created in the first place.

All you need to do is create the icon; oUF will handle hiding it and showing it when needed. Just use the first (original) code block, but change: